1. Field of the Invention
This invention relates to industrial burners and, more particularly, forced draft and regenerative burners that minimize NOx emissions.
2. Description of the Prior Art
Conventional industrial burners are typically configured in a symmetrical fashion. In this symmetrical configuration, a fuel conduit is generally disposed axially along a centerline of the burner and combustion air is generally introduced immediately about a periphery of the fuel conduit or with appropriate air ducting symmetrically about the fuel conduit and radially spaced therefrom. A prior art example of a symmetrical industrial burner is disclosed by U.S. Pat. No. 3,876,362 to Hirose. The symmetrical or axial burner disclosed by the Hirose patent attempts to induce a deflected stream of gas from the burner by providing an air inlet in the burner tile structure. The positive axial mass flux of the air and fuel jets causes a recirculation of products of combustion (POC) from the furnace chamber into the burner tile. This induction of POC into the burner tile and subsequent entrainment into the fuel and air streams causes lower flame temperatures and lower NOx production rates.
An object of the present invention is to provide a burner having reduced NOx emissions. It is a further object of the present invention to provide a burner configuration that maximizes air and fuel entrainment with products of combustion (POC) thereby minimizing NOx formation. It is a specific object of the present invention to provide an oxygen-enriched burner that does not increase NOx emissions, and does not require high-purity source oxygen to achieve low NOx emissions.
The above objects are accomplished with a burner for non-symmetrical combustion made in accordance with the present invention. The burner generally includes a burner housing enclosing a burner plenum. A fuel conduit extends longitudinally within the housing and is positioned coaxial with a line spaced from a central axis of the burner. The fuel conduit defines a fuel exit opening. A baffle defining an air conduit extends longitudinally within the housing. The air conduit has an air opening on an opposite side of the burner central axis from the fuel exit opening. The air opening may be positioned a greater distance away from the burner central axis then the fuel exit opening. At least one oxygen injection lance extends longitudinally within the housing and partially through the air conduit. A burner port block is located adjacent to the baffle and downstream of the air opening and is in fluid communication with the fuel conduit and the air conduit.
The burner port block may have a sidewall diverging downstream of the air opening, and which may diverge at a flare angle of between approximately 2 and 30 The sidewall of the burner port block may diverge from the burner central axis at a flare angle of between approximately 2xc2x0 and 30xc2x0. The air conduit may have a cross-sectional shape in the form of a segment of a circle defined by a chord. The burner may include a plurality of oxygen injection lances symmetrically positioned within the chord-shaped air conduit.
The baffle may further define a primary stabilization cavity immediately adjacent the fuel exit opening. The cavity may be in fluid communication with the fuel conduit through the fuel exit opening. The cavity may be cylindrical-shaped and coaxial with the fuel conduit. A combustion gas conduit may extend through the burner plenum and be connected to the cavity. The burner plenum may be connected to a diverter valve configured to selectively admit combustion gas from the burner plenum into the combustion gas conduit. The fuel conduit may be positioned coaxially within the combustion gas conduit. The baffle preferably separates the burner port block from the burner plenum. The fuel conduit may be positioned coaxially within the combustion gas conduit. Swirl vanes may be positioned within the combustion gas conduit and be peripherally spaced around the fuel conduit.
The burner may further include an auxiliary fuel conduit extending longitudinally through the burner plenum and connected to the burner port block. The auxiliary fuel conduit may define an auxiliary fuel exit opening radially spaced from the fuel exit opening and coterminous with the burner port block. The auxiliary fuel conduit may be positioned on the opposite side of the burner central axis from the air opening.
The present invention is also a method of non-symmetric combustion in the burner generally described hereinabove. In particular, the burner used in said method may include a fuel conduit coaxial with a first axis and defining a fuel exit opening. The burner may further include a baffle defining an air conduit having an air opening. The air conduit may be coaxial with a second axis. At least one oxygen injection lance may extend partially through the air conduit. A burner port block may be located adjacent to the baffle and downstream of the air opening and be in fluid communication with the fuel conduit and the air conduit. The burner port block may have a sidewall.
The method may include the steps of: injecting fuel along the first axis and out through the fuel exit opening, with the first axis spaced from a central axis of the burner; dispersing oxygen into combustion gas; discharging the combustion gas containing dispersed oxygen through the air conduit defining the air opening along the second axis, with the second axis positioned on an opposite side of the burner central axis from the first axis; inducing the combustion gas containing dispersed oxygen to flow toward the sidewall of the burner port block; mixing the combustion gas containing dispersed oxygen with the injected fuel; igniting the mixed combustion gas containing dispersed oxygen and injected fuel; and recirculating products of combustion into the discharging combustion gas containing dispersing oxygen.
The sidewall may diverge from the burner central axis, and the method may further comprise the step of inducing the combustion gas containing dispersed oxygen to flow in a diverging manner along the sidewall of the burner port block. The burner may further include an auxiliary fuel conduit coaxial with a third axis and defining an auxiliary fuel exit opening. The third axis may be radially spaced from the first axis, and the method may further comprise the step of injecting auxiliary fuel along the third axis and out through the auxiliary fuel exit opening in place of the step of injecting the fuel along the first axis.
The method may further comprise the step of dispersing the oxygen into the combustion gas through at least one oxygen injection lance extending at least partially into the air conduit. The air conduit may have a cross-sectional shape in the form of a segment of a circle defined by a chord. The at least one oxygen injection lance may include a plurality of oxygen injection lances symmetrically positioned within the air conduit, such that the step of dispersing the oxygen into the combustion gas through the plurality of oxygen injection lances results in a uniform dispersal of the oxygen into the combustion gas.
Further details and advantages of the present invention will become apparent from the following detailed description read in conjunction with the accompanying drawings, wherein like reference numerals designate like parts throughout.